In recent years, lithium batteries have received a great deal of attention and are used in various portable devices, such as notebook PCs, mobile phones and digital cameras for their small weight, high discharge voltage, long cyclic life and high energy density compared with conventional lead storage batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries.
An anode of a lithium battery should have such properties as high energy density; low open-circuit voltage versus metallic lithium electrodes; high capacity retention; good performance in common electrolytes; high density (e.g. >2.0 g/cm3); good stability during charge and discharge processes, and low cost. At present, the most widely used anode active material is carbonous/carbonaceous material such as natural graphite, artificial graphite and amorphous-based carbon. Amorphous-based carbon has excellent capacity, but the irreversibility thereof is relatively high. The theoretical maximum capacity of natural graphite is 372 mAh/g, but the lifetime thereof is generally short.
In general, carbonous/carbonaceous material anode has low efficiency and cycle performance in the first charge and discharge cycle due to the formation of Solid Electrolyte Interface (SEI) layer. A stable SEI layer is essential in the lithium battery to prevent anode material from reacting with the electrolyte, therefore, the selection of the electrolyte is limited. Only the electrolytes in which a stable SEI layer can be formed are suitable for using in a lithium battery.
Carbon nanotubes are a novel carbonous/carbonaceous material formed by one or more layers of graphite. A distance between two layers of graphite in the carbon nanotube is about 0.34 nanometers, which is greater than the distance between two layers in natural graphite. Thus, carbon nanotube is a suitable material for using as the anode of the lithium battery. However, until now, carbon nanotubes are mixed with a binder and disposed on a current collector of the anode. As such, adsorption ability of the carbon nanotubes is restricted by the binder mixed therewith.
What is needed, therefore, is to provide a cathode of lithium-ion battery that can overcome the above-described shortcomings.